Detachable bit for rock drills



R. S. HART DETACHABLE BIT FOR ROCK DRILLS Filed April 28, 1955 June 18, 1935.

Patented June 18, 1935 UNITED STATES PATENT OFFICE.

DETACHABLE BIT FOR ROCK DRILLS 2 Claims.

The present invention relates to rock drills, and has for its important feature an improvement in the mode of attaching a'separable or detachable drill bit to the drill rod or shank.

It is well known to use detachable drill bits on drill rods of this particular type of rock drill. It is also well known to attach such detachable drill bits to drill rods by threaded studs and similar devices.

The present invention is concerned with a specific improvement in the drill bit means, the stud and its thread form and the resultant threaded seats in the drill bit and rod. As this form of rock drill is of the percussive type and is therefore subjected to extremely rough treatment during use, threaded on drill bits having normal commercial threads of acute or small circular pitch thereon are very often destroyed by reason of the threads, in the socket bores of the drill bit and rod, and on the attaching stud, being sheared off, because of the non-seating of therear face of the drill bit firmly against the seating end face of the drill rod.

If the drill rod and bit are not initially firmly seated together in the case above noted, the first percussive blows of the air hammer, shear the threads, as noted. This destroys the bit and sometimes necessitates the refabrication of the drill rod end. This happening is due to the fact that in commercial threads such as have been heretofore used, the lead or pitch, angle of thread, and the consequent circular angle of the lead or pitch of the helix around the body of the bore or stud is not suited to receive heavy percussive blows.

Under normal conditions of use, threaded studs, bolts and nuts, can maintain the constant load for which they were designed, but when subjected to heavy and rapid percussive forces while in a floating position, i. e. with the held parts not firmly seated, the full force of percussion is undeflected, and is exerted to deform the threads transversely, and then to shear the threads, completely.

The present improvement is devised to prevent the shearing of the threads and in the event of a careless assembly of the drill bit to the rod, in which .the two are not tightly assembled, the coacting threads of attachment between the drill bit and drill rod, upon the starting of the air hammer, do not shear, but act as a camming means, whereby, after a few blows are struck the drill bit and rod are automatically brought together in a tight, impact resisting assembly.

These and other capabilities will be appre- Fig. l is a View in elevation of the present in-' vention, with the drill rod broken away for convenlence;

Fig. 2 is an end view of the drill bit;

Fig. 3 is a fragment of the threaded end of the drill rod, partially sectioned;

Fig. 4 is an elevational view of one form of the connecting stud;

Fig. 5 is an end view thereof;

b -6 a transverse sectional view of the drill Fig. '7 is an enlarged transverse sectional view of one ofthe helices; and

Fig. 8 is a side View of a modified form of the present invention. 1

The structure of the present invention involves three main parts, the steel drill rod 1, the hardened drill bit 2, and the connecting stud 3.

In the structure of Figs. 1 to 5, inclusive there is shown a threaded interconnection between these three parts in which the stud is provided with low angle-faced plural helices, in the present instance six in number as indicated in the end View, Fig. 5. This form of multiple, low anglefaced helix gives an extremelyfast thread so that in the view, Fig. 4, one complete turn of one of the helices l2 gives a circular lead of about 186-" or stud, Fig. 4, indicates that the force of a hammering impact on the stud inthe direction of the vertical axis l5 of the stud, in either direction would freely rotate the stud in its coacting threaded seat in one or both of the parts i and 2.

A series of repeated compressive blows on the shown. .In practice the drill is rotated an increment between each hammer stroke in a clockwise direction as indicated by the arrow at Fig. 2, and the helices on the stud being left handed, this rotation action causes the stud to be rotated in either the rod or the bit a small amount each hammer stroke until the contact surfaces Ill-ll approach and are tightly engaged.

It is understood that the clearances between the' stud helices and the corresponding helical bores in the bit and rod, are such as to permit the stud to have considerable slackness in fit therein, and this feature also enhances the closing up action between bit and rod.

A further feature also adds to the bit and rod closing function, and lies in the form of the helices they being extremely shallow in cross section, as in Fig. 7, wherein the root of the helix i8 is comparatively wide, and its depth 59 is shallow. Thus, the helical thread face presented to its coordinating threaded bore is of a contour that frees it of any wedge action, and aids in causing the stud under end pressures to readily seat itself by self rotation to a point where it is positively stopped and locked.

A further feature of construction is also an aid to the closing up action of the bit and rod, and this relates to the relative length of the stud and the end clearances thereof in the bores of the bit and rod. In Figs. 1, 3 and 6 there is shown that the length of the stud is such that there are ample clearances between the stud ends and the bore ends in bit and rod. The rod clearance [3, Fig. 3, at the end of the bore helices 6 may be so undercut as to leave the helices square ended, below the chamber and in the bit, the clearance M, is also undercut so as to leave the bit helices square ended. When the stud is in mid-position with the surfaces Ill-H in operative locked position, Fig. 1, the clearances |3l4, there shown dotted, are obvious.

By the foregoing noted clearances space is provided at top and bottom of the stud, so that the loosely fitted stud may float up or down within the helical bore 4-5, before the automatic takeup and tightening of the bit and rod takes place. This enables the operator, when assembling the bit and rod together, to insert the stud, and without tools, to partially turn the stud with the fingers to an engaging position of the stud with the bit, then the bit and stud are turned by hand into the helical bore of the rod and thus assembled at or near the operative positions of Fig. 1, or the operation may be reversed. The preferred method is as above noted, as the rod sometimes is of great weight and length, and is not so easily handled as is the drill bit and stud.

After the bit has been used for a period of time and becomes dull and is ready for replacement, it can be loosened by a blow of a hammer, clockwise, as viewed in Fig. 2, by striking on the side of one of the teeth 6, and the bit then turned off by hand and a replacement bit substituted.

As in the usual types of rock drill the present device is provided with a central bore 1 throughout its rod stud and bit length, for the introduction of water to the bit point during drilling.

In the foregoing I have described a stud having multiple helices having pitch lead of about 1 per turn.

While the foregoing describes a helical arrangement of multiple helices of fast pitch, or long lead, I have found that in some instances, a. single helix of somewhat similar cross section as that of Fig. 7, and fully shown in Fig. 8 having a 1 pitch on a stud of about the same diameter as shown in Figs. 4 and 5, also partakes of the same advantages as outlined above for the structure of Figs. 1 to 5. The angle of incidence of the helix on this last described single helix to the axis of the stud, may be the same as that described for the multiple helices or it may be of less pitch. But, in the single thread, long lead, as in the multiple thread, long lead the underlying principle is the same and that is that the long lead angle of the threads are such that longitudinally or axially exerted forces will produce relative rotation of the thread coupled parts, without exceeding the elastic limits of the material of the threads.

It is also practical to use angled helices of wide root and shallow depth having an obtuse angular face and a pitch angle of incidence to the axis of the stud of between about 40 to 48, from the single pitch helix to the six multiple helices, respectively.

By constructing the stud with the helices as above noted, there is provided a strong, damage proof coupling for threaded connections which is unshearable because of its long lead, and which, by virtue of said lead translates end blows into rotative forces instead of shearing forces, and which stud when constructed to coact in a bit and rod having similar, coacting threads, makes a rigid strong, non -loosening, self tightening assembly and at the point where the greatest strains are encountered.

Having thus described my invention what I claim is:

1. The combination with a socket and a hit each having a screw threade'd bore, the screw threads of said bores being of like hand and uniform diameter throughout, and a screw plug with obtuse angle-faced helices thereon fitting said bores and having a screw thread extending uninterruptedly from end 'to end of the plug, said thread having asteep enough pitch so that a longitudinal force will produce relative rotation of the threaded coupling parts.

2. The combination with a socket and a bit each having a screw threaded bore, the screw threads of said bores being of like hand and uniform diameter throughout, and a screw plug fit- RAYMOND S. HART. 

